Fix unreadable repo switcher text in Code Review pane after theme switch (#10600)

[wzc520pyfm]

Description

Fixes #10600.

The repository / branch switcher dropdown at the top of the Code Review pane caches its text color via Dropdown::set_font_color from theme.sub_text_color(theme.background()) once at construction time in CodeReviewState::new (app/src/workspace/view/right_panel.rs). The dropdown view re-renders on Appearance changes, but Dropdown::render_top_bar reads back the cached ColorU instead of re-deriving it from the live theme, so the color goes stale across light ↔ dark switches:

• Open the Code Review pane in dark mode (default) → text color is cached as a near-white (correct against a dark background).
• Switch to a light theme → the dropdown re-renders, but the cached near-white label is now painted on a near-white background → unreadable, exactly the symptom reported in Code review pane: git switcher text is invisible in light mode #10600.
• The reverse direction (light → dark) is the same bug: dark text remains on a now-dark background.

The chevron icon already reacts correctly because its Icon::new(...) color uses unwrap_or_else(|| appearance.theme().active_ui_text_color().into()), which re-derives from the current theme each render. Only the cached font_color path is stale.

This PR subscribes the dropdown to AppearanceEvent::ThemeChanged from its own ViewContext and reapplies the freshly derived color via set_font_color. The derivation is extracted into a repo_dropdown_font_color helper so the construction site and the subscription stay in lock-step. The pattern matches the existing convention used by other selectors in the codebase (e.g. harness_selector.rs, auth_secret_selector.rs, update_environment_form.rs).

The subscription is scoped to the dropdown view, so it is dropped automatically when the Code Review state is torn down (e.g. when the panel is closed) — no leak, no impact on pane-group switching where the dropdown is reused.

Linked Issue

Fixes #10600.

• The linked issue is labeled `ready-to-spec` or `ready-to-implement` (triaged bug, implicitly `ready-to-implement` per CONTRIBUTING.md).
• Where appropriate, screenshots or a short video of the implementation are included below.

Testing

Verified locally with `./script/run` against the exact reproduction steps from the issue:

1. Launch Warp (defaults to dark theme).
2. Open two tabs in two different git repositories so the repo switcher is visible (it only renders when `available_repos.len() > 1`).
3. Open the Code Review pane and confirm the repository name in the top-left dropdown is readable.
4. Switch `Settings → Appearance` to a Light theme without closing the panel.
   • Before this fix: the label is near-white on near-white and effectively invisible.
   • After this fix: the label re-derives a dark text color and stays readable.
5. Switch back to the dark theme — label updates to a light color, still readable.
6. Close and reopen the panel in light mode — label is correct from the start (sanity check that the construction path also still works).

Automated coverage:

• `cargo fmt -- --check` ✓
• `cargo clippy --workspace --exclude warp_completer --all-targets --tests -- -D warnings` ✓
• `cargo nextest run -p warp` — 4011 / 4012 passing. The single failure (`settings::init::tests::test_migration_does_not_rerun_when_marker_present`) reproduces identically on a clean `master` checkout in the same workspace and is unrelated to this change (it's a settings-migration test sensitive to local marker state).

No new automated test added — the regression is a stale cache in a generic `Dropdown` view; asserting it would require either exposing a `font_color` getter on the shared component or building a theme-switch UI test harness, both of which feel disproportionate for a 12-line view-construction fix. Happy to wire up coverage in either direction if reviewers prefer.

• I have manually tested my changes locally with `./script/run`.

Screenshots / Videos

Before:

Fixed:

Agent Mode

• Warp Agent Mode - This PR was created via Warp's AI Agent Mode

CHANGELOG-BUG-FIX: Fix unreadable repository switcher text in the Code Review pane after toggling between light and dark themes.

Co-Authored-By: Warp agent@warp.dev
Co-authored-by: Cursor cursoragent@cursor.com

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@wzc520pyfm

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Overview

This PR fixes the Code Review pane repository dropdown text color by re-deriving the cached dropdown font color when the app theme changes. The implementation keeps the initial color derivation and the theme-change path aligned through a shared helper and follows existing Appearance subscription patterns.

Concerns

• None.

Found: 0 critical, 0 important, 0 suggestions

Verdict

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[vorporeal]

thanks for the fix!